Abstract

Photoabsorption spectroscopy with isolated attosecond pulses provides a means for all-optical time-domain measurement of ultrafast dynamics in bound and quasi-bound states of atoms and molecules, as well as near absorption edges in condensed matter systems. Due to the strong oscillator strength in atoms and molecules in the extreme ultraviolet and soft X-ray spectral regions as well as the high detection efficiency of the transmitted photon signal, attosecond transient absorption spectroscopy is an attractive alternative to traditional photoelectron spectroscopy techniques. We present measurements of the laser-perturbed photoabsorption of helium 1snp singly excited states and quasi-bound autoionizing states of argon with a few-femtosecond autoionization lifetime. In both systems, we observe laser-induced changes in the photoabsorption spectrum which evolve on the single-femtosecond timescale, faster than the laser light oscillation period.

Notes

Acknowledgements

The authors acknowledge helpful discussions and theoretical support from Suxing Hu with regard to the helium experiments and from Chang-hua Zhang, Feng He, and Uwe Thumm with regard to the argon experiments. He Wang is currently at Lawrence Berkeley National Laboratory, Berkeley CA. Baozhen Zhao and Shouyuan Chen are currently at University of Nebraska, Lincoln NE.